Integrated digital circuits can be found in almost any modern electronic device. These integrated circuits perform a large variety of control, monitoring and communication tasks, and thus determine the behavior of the overall electronic device. In the field of digital circuits, the term “sequential logic” generally relates to a class of logic circuits, whose output signal(s) depend(s) not only on the present value(s) of its input signal(s) but also on the previous value(s) of its input signal(s). This is in contrast to so-called combinational logic, in which output signals are a function of only the present input signals. That is, a sequential logic has state (i.e. a memory), which contributes to the value of its output signal(s), whereas combinational logic does not. Sequential logic circuits may be used to construct finite state machines (FSM), and they are a basic function block in all digital circuitry, as well as memory circuits and other digital electronic devices. Virtually all circuits in digital electronic devices include sequential logic.
Sequential logic circuits may be divided into synchronous and asynchronous circuits. In synchronous sequential circuits, the state of the circuit (and thus the output) changes only at discrete times in response to a clock signal. Such circuits are usually referred to as synchronous sequential logic circuits, which operate synchronously to a clock signal. The clock signal(s) may be provided by an external clock device or may be generated on-chip by a complex clock circuit. When the frequency of the clock signal(s) is not within a specific range, malfunction of the logic circuit may be the result.
In many applications, such as for example automotive radar applications (and also in other fields of technology), synchronous sequential logic circuits are used, inter alia, to perform control and monitoring tasks in electronic devices. Therefore, sequential logic circuits may be relevant to security in many applications. In the automotive sector, many electronic devices have to comply with several standards (such as standard ISO 26262 titled “Road vehicles—Functional safety”) with regard to functional safety. Therefore there is a general need to improve or ensure the functional safety of integrated circuits.